Powerware 9390 Installation & Operation Manual page 42

Understanding UPS Operation
The neutral from the system input is connected to the neutral regulator in the DC
capacitors. The output neutral of the system is connected with the required neutral
supplied at the utility bypass input and should never be bonded to ground at the modules
output.
The inverter produces a three phase AC output to a customers load without the use of a
transformer. The inverter derives regulated DC from the rectifier and utilizes IGBT devices
and pulse-width modulation (PWM) to produce a regulated and filtered AC output. The
AC output of the inverter is delivered to the system output through the output contactor
K3.
If the utility AC power is interrupted or is out of specification, the UPS automatically
switches to Battery mode to support the critical load with no interruption. When utility
power returns, the UPS returns to Normal mode.
If the UPS becomes overloaded or unavailable, the UPS switches to Bypass mode. The UPS
automatically returns to Normal mode when the overload condition is cleared and system
operation is restored within specified limits.
If the UPS suffers an internal failure, it switches automatically to Bypass mode and remains
in that mode until the failure is corrected and the UPS is back in service.
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Powerware 9390 UPS (40–80 kVA) Installation and Operation Manual S 164201535 Rev A
®